1. Field of the Invention
This invention relates generally to magnetic tunnel junctions (MTJs) and particularly to reading MTJs.
2. Description of the Prior Art
Magnetic random access memory (MRAM) is foreseen as a candidate for many applications in the coming years. Its non-volatility is attributed to a magnetic tunnel junction (MTJ) making up the primary component of the MRAM because its magnetic orientation switches to save data. However, to gain further acceptance, MTJs must be made to scale.
Currently, programming of the MTJ is achieved by the application of a current through the MTJ for the time duration of ‘t’. For times larger than 5 nano-seconds (ns), the relationship between programming current and time is logarithmic. This region is commonly referred to as the “thermally activated region”. Below 5 ns, the programming current is almost proportional to ‘t’, and this region is commonly referred to as the “processional switching region”.
As the size of the MTJ scales down, which is required for many applications employing high-capacity non-volatile memory, the programming current required for programming or writing to the MTJ decreases. Normally the current required for reading an MTJ is a small fraction of the program current. This is needed to prevent accidentally programming the MTJ during the read operation and is commonly referred to as “read disturbance”. Read disturbance obviously leads to defective MRAMs and can not be tolerated. With the MTJ scaling to small sizes, the required programming current goes down, which increases the probability of read disturbance. At the same time for larger and faster dice, the read current requirements increase. At some point, these two competing requirements make it difficult to prevent read disturbance leading to unintentional programming during read operations and therefore unreliability of the memory.
What is needed is a magnetic random access memory (MRAM) including magnetic tunnel junction (MTJ) with increased reliability particularly during reading operations.